1. Field of the Invention
The present invention is directed to an acoustic delay line for electrical signals of the type having two electrode structures applied on a monolithic piezoceramic substrate forming the electro-acoustic transducers for the delay line, at a distance relative to each other which defines the transit time, and thus the delay line, path.
2. Description of the Prior Art
A delay line having two electrodes on a piezoceramic substrate forming the electro-acoustic transducers of the delay line is described in "Analysis of Broadband Lamb-Wave Delay Lines," Visintini et al., IEEE Ultrasonics Symposium, 1986, pages 315-319. Symmetrical electrode structures are applied to opposite sides of a piezoceramic lamina. The piezoceramic lamina is polarized in the direction of its thickness, so that the transducers generate symmetrical Lamb waves of zero order. Given high signal bandwidths, the dispersive transmission behavior of the Lamb waves has a negative influence, i.e., the acoustic propagation speed of the Lamb waves is dependent on the frequency. Moreover, there are a plurality of Lamb modes having different propagation properties for each frequency range. The selective excitation of the fundamental mode therefore requires the electrode structures to be manufactured with very close tolerances.